1. Field of the Invention
The present invention relates to a reel-up for reeling a fiber web where the fiber web to be reeled and a supporting body form a reel nip.
Further, the present invention relates to a method for reeling a fiber web in a reel-up, the method comprising the step of forming a reel nip between the fiber web to be reeled and a supporting body.
The present invention also relates to a measuring unit, which is arranged for detecting load signals being a function of a linear load of a reel nip (15) of a reel-up.
2. Description of Related Art
When manufacturing paper in a paper machine, papermaking stock is formed into a web, which is dewatered, dried and then wound onto reel spools in order to form paper reels. As a rule, each finished paper reel, normally called a parent roll, is stored for a short period of time in order to subsequently be rewound and converted into more refined products.
In general terms, it is of vital importance that the winding is performed such that each parent roll is clear of defects which can disturb the converting. Ideally, the parent roll should have a circular cylindrical shape, i.e. exhibit a circular cylindrical envelope surface and two end surfaces which are flat and orthogonal to the envelope surface. Furthermore, the parent roll should be dimensionally stable, i.e. adjacent winding layers should not slide against each other so that the paper reel is deformed. In order to achieve this, the web should be wound in a controlled way and with a predetermined web tension in the longitudinal direction of the web throughout the entire paper reel. The web tension should be sufficiently high in order to produce the required friction between adjacent winding layers and to thereby prevent these from sliding against each other. At the same time, the web tension should not be so high that it destroys the paper properties produced in the paper machine. This is especially a problem when manufacturing soft and bulky tissue paper.
Normally, the winding is performed such that the paper reel being wound onto the reel spool abuts against some kind of supporting body during at least a part of the winding sequence. Thereby, the supporting body has the double task of driving the paper reel, as well as defining a reel nip together with the paper reel through which the web passes before it is wound up. It is general knowledge within the technical field that the linear load in the reel nip is an important parameter for controlling the web tension in the paper reel. When manufacturing tissue paper, however, it is desirable to have a linear load which is as low as possible in order to preserve the properties of the tissue paper. When manufacturing such paper grades, it therefore happens that the reel spool is equipped with a centre drive, wherein the linear load in the reel nip can be reduced and the web tension instead is controlled, entirely or partially, by means of modulating the rotational speed of the reel spool in relation to the web speed.
When manufacturing very soft and bulky tissue paper, however, it has proved to be difficult to dispense entirely with the web tension control function being provided by the reel nip. This is true particularly for so called through air dried tissue paper, and at the higher and higher winding speeds and larger parent roll diameters sought for in modern reel-ups. Instead, the design of the supporting body and the method of measuring and controlling the linear load in the reel nip have been developed further. Thereby, the development has gone from hard to soft reel nips, and towards more and more sophisticated methods of measuring and controlling the linear load in the reel nip.
The published documents WO 2004/110909, WO 2005/077796 and EP 0658504 all describe reel-ups in which the supporting body is made up of an endless belt. The belt can for example be a felt or a wire. During the reel-up the tension of the belt is regulated, which in turn influences the linear load in the reel nip.
EP 0860391 describes a reel-up in which the supporting body is made up of a plurality of endless belts being arranged one beside the other in the cross direction of the fiber web, and being individually adjustable in order to enable profile regulation of the linear load in the reel nip.
U.S. Pat. No. 5,901,918 discloses an apparatus for winding a paper reel. The winding apparatus is especially adapted for winding bulky tissue paper and comprises a supporting body in the form of an endless belt, which extends unsupported between two guide rolls. During the winding, the paper reel abuts against the belt at a point along the unsupported distance, wherein the paper reel deflects the belt and forms a soft reel nip with the belt. Accordingly, the deflection is a measure of the linear load in the reel nip. Furthermore, the winding apparatus includes a deflection sensor, which is arranged inside the belt loop for measuring the deflection of the belt, preferably by means of an optical system, ultrasonic system or another contactless system. In spite of the fact that the device according to U.S. Pat. No. 5,901,918 generally is working well, it can be mentioned in this dontext that contactless measurement, as a rule, exhibits the disadvantage that for example dust, water vapour, or the like, easily disturbs the measurement. The present invention tries to solve this problem.